Comment by rkeene2
I also understood the title to mean writing an assembler rather than writing assembly language code, and I've never heard anyone refer to writing assembly as writing assembler (or heard anyone who writes assembly referred to as an "assembly code maker", nor anyone who writes in any language referred to as an "<language> code maker").
I could imagine such phrasing being done by non-native English speakers, of which I'm have no doubt that there are a significant number.
My (unresearched) guess is that this is simply different dialects of speakers emerging with respect to informal references over the decades.
Using “assembler” instead of “assembly” was common enough back in the day that there was no confusion. There were 100x more people writing “assembler” than writing actual “assemblers” so you know, the odds were good.